"They not only provide a completely fresh and detailed view of an area famous to fans of space myths worldwide, but also provide an impressive close-up over an area of great interest for planetary geologists."

Chicarro and his team say the high-resolution images further confirm what NASA scientists have been saying for years: it's not a face, but a raised, eroded surface.

NASA's chief scientist for Mars exploration Dr Jim Garvin describes the formation as the equivalent of a butte or mesa.

Such formations are common in the Mars region of Cydonia, which is located between the planet's southern highlands and northern plains.

Convincing the true believers

But then, some may never be convinced.

Since the spooky, face-like structure was first photographed by NASA's Viking 1 Orbiter 30 years ago, the site has been the subject of breathless speculation.

In movies, books and on the web, some have argued this is a massive sculpture built by intelligent life and that surrounding conical-like structures are pyramids, or remnants of a great city, built by a complex civilisation.

Attempts to say the face is just an accident of geology are often met by claims that scientists have something to hide.

For example, in response to the NASA images released in 2001, web author Richard Hoagland retorted:

"The reality is that it is highly unlikely that any of us would recognise a picture of our own grandmother if it was stretched horizontally, flattened, compressed and shown upside down. So of course it doesn't look much like a face."

'Skull' on Mars

In addition to the well-known face and 'pyramids' in the region, a previously unseen skull-shaped structure also appears in some of the new Mars Express images.

Some may be eager to offer up theories to explain this new site.

Garvin, for his part, doesn't want to discourage anyone from coming up with their own explanations.

"Please realise that as a scientist of Martian landscapes, my position is that of a traditional scientist, and requires that I utilise the paradigms associated with multiple-working hypotheses grounded in the physics of landscape development," he says.

"Other opinions on the basis of other approaches are of course welcome and encouraged."

Alien face or eroded surface, the face on Mars is of interest to planetary geologists like Garvin and these latest images reveal new geological details.

The latest images show the beginnings of what are called debris aprons, or gentle landslides, surrounding hills. Since the debris apron around the face is minor, the scientists suggest former, larger debris aprons may have been covered by lava flows.

Meanwhile, the photographs show that the western wall of the face appears to have moved down as a huge mass. The same massive rock movements can be seen at the base of the surrounding pyramid-like formations.

As for the skull-like formation, Chicarro and his team suggest this is the remnant of an eroded massif. That's their theory, at least.